Final answer:
In cases lacking an obvious DNA source or transfer mechanism, in-depth comparison and secondary evidence are used to establish a link between the DNA and a potential source.
Step-by-step explanation:
When reporting on cases involving DNA evidence where there is no obvious source or transfer mechanism, guidance suggests a thorough investigation to establish a connection between the DNA and its potential source. This may involve comparing the DNA sequences of the sample with known DNA profiles, considering the possibility of secondary transfer, and using additional lines of evidence to build a robust case. The comparison can show whether there is a match, suggesting a link between the evidence and the individual in question. Forensic scientists have even used DNA evidence in immigration cases, as was the case with Dr. Alec Jeffreys' pioneering work on DNA fingerprinting that helped verify family relationships in a precedent-setting case.